This plugin is used for displaying thin vertical lines at each indentation level for code indented with spaces. For code indented with tabs I think there is no need to support it, because you can use :set list lcs=tab:\|\ (here is a space).

Requirements:
This plugin takes advantage of the newly provided conceal feature in Vim 7.3, so this plugin will not work with lower versions of Vim.

Installation:
To install the plugin just put the plugin files in your ~/.vim (Linux) or ~/vimfiles (Windows).

If you use a plugin manager you can put the whole directory into your ~/.vim/bundle/ directory (Pathogen) or add the line Bundle 'Yggdroot/indentLine' to your .vimrc (Vundle).

Customization:
You can change the color of indentLines:
for Vim, set g:indentLine_color_term in your .vimrc, e.g. let g:indentLine_color_term = 239,
for GVim, set g:indentLine_color_gui in your .vimrc, e.g. let g:indentLine_color_gui = '#A4E57E'

You can also change the indentLine char:
for both Vim and GVim, set let g:indentLine_char = 'c' where 'c' can be any ASCII character. You can also use one of ¦, ┆ or │ to display more beautiful lines. However, these characters will only work with files whose encoding is UTF-8.